Life expectancy has declined for many women in the United States, largely due to smoking-related diseases and obesity, a study published Tuesday showed.

Nearly one in five US women saw the number of years they are expected to live decline or hold steady, starting in the 1980s, showed the joint study by the Harvard School of Public Health and the University of Washington.

The study looked at data from more than 2,000 county "units" between 1959 and 2001.

In around 1,000 of those counties -- mainly poor, rural areas -- life expectancy for women dropped starting in the 1980s, "primarily because of chronic diseases related to smoking, overweight and obesity, and high blood pressure," according to the study.

In the United States as a whole, in contrast, life expectancy for women rose by more than six years and for men by more than seven years during the same period, it showed.

"There is now evidence that there are large parts of the population in the United States whose health has been getting worse for about two decades," Majid Ezzati, associate professor of international health at the Harvard School of Public Health, and lead author of the study, said in a statement.

Worst affected by the downturn in longevity were the south -- the region hardest hit by poverty, according to the US Census Bureau -- the Appalachians, southern parts of the Midwest and areas of Texas.

Men in the same areas also saw a drop in life expectancy, but numbers were less alarming than among women -- only four percent -- and the fall was attributed to different causes, mainly HIV/AIDS and homicide.

"Life expectancy decline is something that has traditionally been considered a sign that the health and social systems have failed, as has been the case in parts of Africa and Eastern Europe," said the study's co-author Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington.

"The fact that this is happening to a large number of Americans should be a sign that the US health system needs serious rethinking," he added.